Click URL to open PWA automatically

Hi Noel Burgess 

Here are a couple of sample apps with working configuration for URL handling.
Hello! (luhuangmsft.github.io)
Hello! (mandymsft.github.io)

From then DevTools Application pane, you can see that their manifests contains "url_handlers" entries:
https://luhuangmsft.github.io/pwa/manifest.json
https://mandymsft.github.io/pwa/manifest.json

web-app-origin-association files that complete the handshake:

https://luhuangmsft.github.io/.well-known/web-app-origin-association
https://mandymsft.github.io/.well-known/web-app-origin-association

mandymsft.github.io/pwa is able to handle links from luhuangmsft.github.io/pwa but not vice versa. 

To test this behavior, you should:
* use Edge 91 or above
* enable #enable-desktop-pwas-url-handling from edge://flags

* configure the browser installation to be the default web browser in system settings
* install one or both of the sample apps

* Test with a link in other applications, a URL in run.exe (Win+R), or a URL as a command line argument. 
* Eg. $ msedge.exe https://luhuangmsft.github.io/pwa/